There is a significant advantage to the use of alternating current (AC) power lines for purpose of communication between electronic devices using a power line communication system. Such a power line communication system can be used for monitoring and controlling basic function including energy management, security, and safety control in applications including homes, factories, offices, automobiles and aircraft. Use of existing power lines as a communication medium eliminates installation costs for adding dedicated communication wiring to existing structures.
Prior art power line control systems have been developed for activating and deactivating devices via the power line connection. Success of these prior art control systems has been limited because of their inability to provide a robust and reliable communication system.
One reason for the failure of prior art designs to provide a viable power line communication system is the adverse environment in which power line communication must take place. A typical AC power line network is used for power distribution to a number of electric devices connected thereto. Such devices cover a wide range of applications including hair dryers, television sets, computers and specialized factory tooling. Each type of device conducts a significant level of noise back onto the power lines. Different devices produce different types and degrees of noise. This diverse power line noise problem severely impairs the proper and reliable operation of any power line communication system.
Another problem hindering any power line communication system is signal attenuation. Due in part to the diverse impedance levels of the electric devices being used with a power line network, transmitted communication signals may suffer greater than 40 dB attenuation before being captured by a receiver. The significant signal attenuation problem in combination with the noise problem renders effective signal line communication difficult.
One particularly troublesome source of power line noise is the ubiquitous television set commonly used in the United States, Europe and worldwide. While television sets do not produce the largest magnitude of noise interference on power lines, they do affect a significant percentage of existing power line networks. Raster scan type television sets produce a pulsed power line interference. Each noise pulse corresponds to the completion of a scan line. In television sets conforming to United States' standards, each noise pulse occurs at approximately 15.734 KHz intervals. In European television sets, noise pulses occur at approximately 15.625 KHz intervals. Harmonics of this interference can extend up into the Megahertz region. This television set interference along with signal attenuation are significant reasons for the failure of the prior art to effectively develop a powerful and a reliable power line communication system. A better means and method is needed for implementing a reliable power line communication system while avoiding determinable interference harmonics.